1. Field of the Invention
The present invention relates to an RFID (Radio_Frequency_IDentification) tag for exchanging information with an external device in a noncontact manner. There are the cases where those in the art refer to the “RFID tag” used herein as an “RFID tag inlay” regarding it as an inlay for the “RFID tag.” There are also the cases where the “RFID tag” is referred to as a “Radio Frequency Identification.” The “RFID tag” also includes a noncontact IC card.
2. Description of the Related Art
In recent years, there have been proposed various kinds of RFID tags for exchanging information with an external device represented by a reader-writer in a noncontact manner via radio waves. There has been proposed a kind of the RFID tag having a configuration in which an antenna pattern for radio communication and an IC chip are mounted on a base sheet consisting of plastic or paper (see, for example, Japanese Patent Laid-Open No. 2000-311226, Japanese Patent Laid-Open No. 2000-200332, Japanese Patent Laid-Open No. 2001-351082). A conceivable form of use for such a type of the RFID tag is to attach it to an article or the like and exchange the information on the article with the external device to identify the article.
FIG. 1 is a plan view showing an example of the RFID tag.
An RFID tag 1 shown in this FIG. 1 is configured by an antenna 12 provided on a base 13 consisting of a sheet-like PET film and the like and an IC chip 11 electrically connected to the antenna 12 by gold, solder or the like and firmly fixed to the base 13 by an adhesive.
The IC chip 11 configuring the RFID tag 1 can perform radio communication with the external device via the antenna 12 and exchange information.
Here, FIG. 1 shows a looped antenna as the antenna 12 of the RFID tag 1. As for the RFID tags in general, however, the antenna 12 is not limited to this form. It is possible to adopt the antennas in various forms such as the antenna in the form having the IC chip 11 at its center and linearly extending to both sides from the IC chip 11.
The RFID tag as described above may have its communication performance significantly deteriorated by a piece of metal or the like if one exists in proximity thereto. To prevent this, an RFID tag called a metal tag is known. The metal tag is an RFID tag of a structure having a substrate surrounded by a metal pattern operating as the antenna, where the communication performance is maintained even if another piece of metal or the like approaches except for a portion in which the piece of metal becomes a shadow.
Here, a conventional manufacturing method of the metal tag will be described.
FIGS. 2A and 2B are perspective views of parts used for manufacturing of the metal tag.
Here, the IC chip 11 (FIG. 2A) and a substrate 20 for the metal tag (FIG. 2B) are prepared.
As shown in FIG. 2A, the IC chip 11 has a bump 11a of gold or the like formed on its connecting terminal. In FIG. 2A, the IC chip 11 is shown upside down as compared to the IC chip 11 shown in FIG. 1 in order to show a forming face of the bump 11a. The IC chip 11 has a function of performing radio communication with an external device via the antenna (described later) and exchanging information (refer to FIG. 1).
The substrate 20 has a metal antenna pattern 22, which operates as the antenna after assembly, formed on a dielectric plate 21 and surrounding it except for a portion 23 on which the IC chip 11 is to be mounted.
FIGS. 3A, 3B and 3C are process drawings showing an example of the manufacturing method of the metal tag.
Here, a liquid or sheet-like underfill 24 which is a thermosetting adhesive is supplied to the portion 23 of the substrate 20 on which the IC chip 11 is to be mounted (FIG. 3A). The IC chip 11 is put on the portion 23, and the substrate 20 and the IC chip 11 are sandwiched by a heating stage 31 and a heating head 32 to be heated and pressed. Thus, the IC chip 11 and the metal antenna pattern 22 are electrically connected via the bump 11a, and the IC chip 11 is fixed on the substrate 20 as the underfill 24 (FIG. 3B) hardens.
The RFID tag of the structure shown in FIG. 3C is manufactured by undergoing such a process flow. The RFID tag performs radio communication with the external device by means of the IC chip 11 via a loop antenna in the form surrounding and circling front and rear faces of the dielectric plate 21.
This type of the RFID tag is referred to as a so-called metal tag, where the communication performance is sufficiently secured as to the front side of the substrate 20 on which the IC chip 11 is mounted even if another piece of metal approaches the rear side opposite to the front side on which the IC chip 11 is mounted.
However, the RFID tag formed by the manufacturing method described with reference to FIGS. 2 and 3 has the IC chip 11 mounted on the substrate 20 projected from the front face of the substrate 20, which is difficult to render flat and thin. To solve this, it is supposedly possible to render thickness of the substrate 20 thinner. However, a certain distance is required between the substrate front face portion and the substrate rear face portion of the metal antenna pattern 22 in order to secure expected performance of the metal antenna pattern 22 as the loop antenna. Therefore, there is a limit to rendering the substrate 20 thinner from the viewpoint of securing antenna performance.